(a) Field of the Invention
The present invention relates to a system and method of stabilizing combustion in a hybrid electric vehicle. More particularly, the present invention relates to a system and method of stabilizing combustion in a hybrid electric vehicle that reduces emission of noxious gases by discharging an exhaust gas remaining in an exhaust gas recirculation line during starting or stopping the vehicle engine.
(b) Description of the Related Art
Typical vehicles convert energy generated by burning fossil fuel into kinetic energy and run by expending the kinetic energy. An exhaust gas generated by burning the fossil fuel is discharged to the atmosphere through a tail pipe after the exhaust gas is processed to remove noxious materials. Vehicle exhaust systems may include a catalytic converter for processing noxious materials contained in the exhaust gas.
Recently, environmentally-friendly vehicles such as electric vehicles and hybrid electric vehicles have been developed and used due to depletion of fossil fuels and environmental pollution caused by fossil fuel vehicles. In addition, new catalysts have been developed for use in processing noxious materials contained in the exhaust gas.
Hybrid electric vehicles typically use an engine and a motor/generator as power sources. The hybrid electric vehicles use the motor/generator, which has better low-speed torque characteristics, as a primary power source at low speeds, and use the engine, which has better high-speed torque characteristics, as a primary power source at high speeds. Because hybrid electric vehicles use a motor/generator rather than the fossil fuel burning engine at low speeds, they consume less fuel and produce less exhaust gas.
The vehicles may also contain an exhaust gas recirculation (“EGR”) module to reduce production of nitrogen oxides and improve fuel economy by lowering the combustion temperature and for reducing production of nitrogen oxides. The EGR module is mounted on a recirculation pipe fluidly connecting an exhaust pipe with an intake manifold or an intake duct and recirculates a portion of the exhaust gas back into the intake manifold or the intake duct to lower maximum temperature during combustion.
The EGR module operates in a predetermined engine operation region. When the EGR module is not operating, some exhaust gas can leak through a gap between the EGR module and the recirculation pipe. When the engine is running, the leaked exhaust gas is directly supplied into a combustion chamber. Because the amount of leaked exhaust gas is very small, however, combustion is little affected by the exhaust gas leaking into the combustion chamber.
If the engine is not operated for a long time, however, the leaked exhaust gas collects in the recirculation pipe between the exhaust gas recirculation module and an intake system (intake manifold or intake duct). The leaked exhaust gas gathered in the recirculation pipe (hereinafter referred to as ‘residual gas’) is supplied into the combustion chamber when the engine is started, which causes unstable combustion and increases the production of noxious materials in the exhaust gas. Particularly, because the catalyst in the catalytic converter cannot reach its activation temperature when the engine is started after a protracted period of downtime, the catalytic converter cannot effectively process the noxious materials in the residual gas and they are discharged to the exterior of the vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.